Dispersion of light through a prism
In a prism, material dispersion (a wavelength-dependent refractive index) causes different colors to refract at different angles, splitting white light into a rainbow.
The splitting of a ray into its component colours is known as dispersion of light and the band of colours is known as a spectrum.
Formation of a rainbow - dispersion
A rainbow is formed when white light is dispersed through raindrops.
Dispersion of light
Sky is blue and leaves are green. To the physicist, the colors of objects are not
in the substances of the objects themselves or even in the light they emit or reflect.
Color is a physiological experience and is in the eye of the beholder. So when we
say that light from the sky is blue, in a stricter sense we mean that it appears
blue. Many organisms, including people with defective color vision, will not see
the sky as blue at all.
When a beam of sunlight or white light falls on a prism, we will observe that it
gets separated as different band of colours. These colours are V(violet), I(indigo),
B(blue), G(green), Y(yellow), O(orange), R(red) ––– VIBGYOR. This shows
that the beam of white light is actually a composite of seven different colours.
Each colour has a particular wavelength and frequency.
This phenomenon of dispersion was first discovered by Newton. He also passed each
individual coloured light through another prism, and concluded that each colour
has no other component. Thus a ray of yellow light is composed of yellow colour
only. Similarly a ray of blue or red light will have only blue or red colours. A
white light is a mixture of all seven colours.
When light rays fall on a material, they can undergo any of the
phenomenon like transmission (refraction), absorption or reflection. If the light falling on the material passes through it completely, we say that the
material is transparent. If all the light falling on an object is absorbed, then
it will appear black to our eyes. If all the light is reflected (no absorption),
the object will appear in the same colour as the colour of the light beam. For example
if white light is falling on the object then the object will appear white.
Exercise:Try it yourself
Try and do a simple experiment. Take a square of black paper and another square
of white paper. Keep them side by side near a wall. Make the room dark. Now flash
a torch on the two pieces so that the light scattered will hit the wall. What will
you observe? You will see that the white square is reflecting a lot of light whereas
the black square is not. This simple experiment demonstrates the fact that black
colour absorbs all the light falling on it and that white colour reflects all the
light falling on it.